Trolley jacks are categorised according to the maximum working load they are able to lift. This is measured in tonnes with trolley jacks available from 0.5 tonne (500 kg) to 10 tonnes (10000 kg).
Trolley jacks contain an overload protection system which is located inside the hydraulic system. If the jack is being overloaded, the check valves open and permit oil to draw away from the main piston when pressure exceeds a set limit, allowing the jack to only lift its maximum weight capacity and no more.